Application of the spline-function method to determination of potential constants for diatomic molecules

We describe a new technique for calculating force constants for diatomic molecules, making significnat use of approximate information on derivatives of the function of the total energy of the molecule given in tables. The proposed procedure is applied to determine the potential constants for the LiH molecule.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 98–101, January–February, 1985.     

Cathodic Hydrogen Evolution from Aqueous Solutions of Acetic Acid

In continuation of the work on establishing hydrogen donors in the hydrogen evolution reaction from different acid molecules, cathodic evolution of hydrogen on silver is investigated from solutions of monobasic acetic acid with the aim to establish the origin of reduced hydrogen. Solutions of 0.2 M acetic acid with 0.2 M perchloric acid, neutralized to different pH values by NaOH, are used. The earlier established criterion is used for discerning between two possible hydrogen evolution mechanisms: (1) from dissociated hydrogen ions and (2) from undissociated hydrogen atoms in the molecule. At medium pH values, the undissociated acid molecules participate as hydrogen donors. Rate constants for reactions 1 and 2, evaluated at a potential of –800 mV (SCE), at which the entire pH range can be scanned, are 2.9 × 10^–6 and 1.9 × 10^–8.     

From the Periphery: the genesis of Eugene P. Wigner's application of group theory to quantum mechanics

This paper traces the origins of Eugene Wigner's pioneering application of group theory to quantum physics to his early work in chemistry and crystallography. In the early 1920s, crystallography was the only discipline in which symmetry groups were routinely used. Wigner's early training in chemistry, and his work in crystallography with Herman Mark and Karl Weissenberg at the Kaiser Wilhelm institute for fiber research in Berlin exposed him to conceptual tools which were absent from the pedagogy available to physicists for many years to come. This both enabled and pushed him to apply the group theoretic approach to quantum physics. It took many years for the approach first introduced by Wigner in the 1920s – and whose reception by the physicists was initially problematical – to assume the pivotal place it now holds in physical theory and education. This is but one example that attests to the historic contribution made by the periphery in initiating new types of thought-perspectives and scientific careers.     

NMR spectra, structure, and stereochemistry of grossheimin

Summary 1. The chemical shifts and coupling constants of all the protons in the grossheimin molecule have been found with the aid of double and triple resonance and also by the INDOR method.2. The position of the oxo group at C₂ in grossheimin has been confirmed.3. The configuration and conformation of the grossheimin molecules have been determined.All-Union Scientific-Research Institute of Medicinal Plants. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 724–730, November–December, 1972.     

On the role of solvent in complexation equilibiria. II. The acid-base chemistry of some sulfhydryl and ammonium-containing amino acids in water—acetonitrile mixed solvents

The macroscopic and microscopic acid-base chemistry of a series of sulfhydryl and ammonium-containing amino acids HS–R–NH₃ [R=–CH₂CH(COOH)–, cysteine (CYS); R=–C(CH₃)₂CH(COOH)–, penicillamine (PEN); R=–CH(COOH)CH₂CH₂CONHCH(–CH₂)CONHCH₂COOH, glutathione (GSH)] was characterized in water and its binary mixtures with acetonitrile (16.3, 34.2, and 53.9 mass % acetonitrile). Macroscopic acid dissociation constants were obtained by potentiometric titration using the glass-calomel electrode pair. Microscopic acid dissociation constants were calculated from ultraviolet absorption measurements at ca. 232 nm where the deprotonated sulfhydryl group absorbs. The macroscopic constants decrease uniformly as the solvent becomes enriched in acetonitrile. The microscopic constants, which characterize the relative concentrations of the two monoprotonated tautomers of the molecules (I and II) reveal that as the solvent becomes enriched in acetonitrile, the fraction of molecules existing as highly charged tautomer I decreases for CYS (0.68–0.40), PEN (0.85–0.34), and GSH (0.61–0.30). These results are related to the decreasing concentration of water as the solvent becomes enriched in acetonitrile.     

Investigation of the association of aromatic dyestuff molecules in aqueous solution by1H NMR

We have studied experimentally the proton chemical shifts of the molecules of Acridine Orange and proflavine in aqueous solution as a function of the.concentration of the aromatic ligands. A method is proposed for determining the chemical shifts of the protons in associations from the observed concentration dependence of the proton chemical shifts of dyestuff molecules in solution, which can be used at fairly high concentrations of the interacting molecules. The association constants of the dyestuff molecules and the proton chemical shifts in the association have been calculated. The proton shifts obtained have been used toether with a model of the ring currents to determine the most probable structure for the 1:1 molecular complexes of Acridine Organce and proflavine in aqueous solution.Sevastopol Institute for Instrument Construction. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 83–89, January–February, 1991. Original article submitted February 2, 1988.     

The role of charge transfer in the stripping of a hydrogen atom by peroxide radicals

Transition states of the reactions of hydrogen atom stripping by a formylperoxide radical from propylene and formaldehyde molecules were calculated in the MINDO/3 (UHF) approximation. A parameter characterizing the reactivity of reagents, which is a linear function both of the electronic properties of the reacting particles and of the reaction rate constants, is proposed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 1, pp. 37–40, January–February, 1993.     

Calculating the rate of attainment of a given critical configuration in a linear molecule

A study has been made of the rate of monomolecular reaction in a linear molecule as a function of the number of atoms in the molecule for various boundary conditions. The interactions between the atoms are assumed harmonic, while the atomic masses and bond rigidities may take any values. The studies are based on the theory of the activated complex and Slater's theory. It is found that the frequency with which the critical distance between adjacent atoms is attained ceases to be dependent on the number of atoms for very long molecules with any boundary conditions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 650–655, November–December 1986.We are indebted to A. V. Baklanov, A. A. Zharikov, and B. I. Yakobson for useful discussions and valuable comments.     

Electron Diffraction Determination of Equilibrium Structure for Rigid Molecules. Equilibrium Configuration of 1,2-Thiaarsol According to Gas-Phase Electron Diffraction and Quantum-Chemical Data

For rigid polyatomic molecules, a procedure is described for determining their equilibrium geometrical structures by processing gas-phase electron diffraction, spectroscopy, and quantum-chemical data. The efficiency of the procedure is demonstrated by reference to the 1,2-thiaarsol molecule. For this molecule, quantum-chemical calculations of different degrees of complexity have been carried out, and harmonic and anharmonic force fields have been constructed. The force constants were employed for determining the equilibrium geometry from experimental data. Analysis of the results of this study suggests that the calculated vibrational corrections to the internuclear distances are almost independent of the level of the quantum-chemical calculations.Original Russian Text Copyright © 2004 by Yu. I. Tarasov, I. V. Kochikov, D. M. Kovtun, N. Vogt, B. K. Novosadov, and A. S. Saakyan__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 822–829. September–October, 2004.     

Sorption and Diffusion of SF6 in Silicalite Crystals

Kinetic and equilibrium data for sorption of SF₆ in silicalite have been determined by the ZLC method. The equilibrium constants and adsorption energy are comparable with the values reported previously for SF₆-NaX. Intracrystalline diffusion is relatively rapid with diffusivities of order 10_–7– 10^–8 cm²·s^–1 at temperatures in the range 30–90°C. The implications for the use of SF₆ as a probe molecule for assessing the integrity of silicalite membranes are considered.     

An NMR study of proton exchange in the system p-nitrosophenol—p-quinone monooxime

The solvent used was dimethylformamide at neutral and alkaline pH. The equilibrium constants are determined by spectrophotometry. The rate of proton exchange has been measured as a function of temperature and concentration. The rate constants and activation energies have been measured; for uncatalyzed exchange k_n=(1.5±0.5) ·· 10³ M^–1 sec^–1, E=8±1 kcal/mole, while base-catalyzed exchange has k=(0.3±0.1) · 10⁶ M^–1 sec^–1 and E=6±1 kcal/mole.We are indebted to A. I. Brodskii for assistance in this work, and to V. I. Oshkaderov and L. A. Kichakova for recording the NMR spectra.     

Nitration equilibrium of water-soluble carboxycellulose

Maximum and minimum values of the equilibrium constants for nitration of hydroxyl groups in water-soluble carboxycellulose (WSCC) have been estimated. Electronegative substituants and elements of the cellulose structure in the WSCC molecule substantially lower the equilibrium constants for nitration compared with those for polyatomic aliphatic alcohols.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2254–2258, October, 1991.     

Infrared diode laser spectroscopy of the ν = 2 band of AlF

A vibrational–rotational spectrum of the ν = 2 transitions of a high-temperature molecule AlF was observed between 1490 and 1586 cm⁻¹ with a diode laser spectrometer. Measurements were made on the ν = 3–1, 4–2, 5–3 and 8–6 bands at a temperature of 900 °C. Measured spectral lines were fitted to effective band constants ν₀, B_ν and D_ν for each band. Present measurements were made with only one Pb-salt laser diode. Physical significance of the effective band constants is discussed.     

Theoretical investigation of the structure and vibrational spectrum of the Li2CO2 molecule

The special features of the potential-energy surface (PES) and the paths for the intramolecular rearrangements of the Li₂CO₂ molecule have been investigated by the SCF method in the double-zeta Huzinaga—Dunning basis supplemented by d-type polarization functions in the carbon and oxygen atoms (DZ + P). It has been shown that there are two minima, which correspond to C_s and C₂ structures, on the PES of the molcule. All the remaining structures of the molecule considered either correspond to saddle points or do not represent special points on the PES at all. The force constants, vibrational frequencies, and intensities of the vibrational transitions in the IR spectra have been calculated for both isomers in the DZ basis. The theoretical values of the vibrational frequencies and the isotope shifts are in good agreement with the experimental data obtained with matrix isolation: the mean deviation of the scaled theoretical frequencies for the C_s isomer amounts to 13 cm^–1 or 1.6%. An analysis of the Mulliken populations, as well as a comparison of the geometric parameters and force constants of the isomers of Li₂CO₂ with the corresponding parameters of the Li₂O and CO molecules and of the CO₂ ^2– ion, have shown that the chemical bonds in both isomers may be represented by the scheme (Li⁺)₂CO₂ ^2–. The similarity between the PES's of the Li₂CO₂ and Li₂CO₃ molecules has been demonstrated and explained in the framework of the Gillespie—Nyholm model.Ivanovo Chemical-Engineering Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 30–38, March–April, 1991.     

Synthesis and properties of charge-transfer complexes based on quaternary salts of amines and tetracyanoquinodimethane

The electrical and optical properties of four charge-transfer complexes based on a molecule of tetracyanoquinodimethane (an acceptor) and donor molecules of quaternary salts of amines have been studied. It has been shown that the conductivity of the complexes has a semiconductor character and is determined by conduction along stacks of tetracyanoquinodimethane molecules.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 102–105, January–February, 1986.     

Antiradical activity of the hormonal preparation estrone in lipid models undergoing oxidation

The rate constants and stoichiometric coefficients of chain termination in the oxidation of lipid models (methyl esters of acids of the oleic series: cis-6-, cis-9-, trans-9-, and trans-11-C₁₇H₃₃COOCH₃) by the main representative of the follicular hormones — estrone (313–348 K) — and for comparison by the phenol 2,6-ditert-butyl-4-methylphenol (323.15 K) were measured. The strength of the OH bond in the estrone molecule was estimated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 5, pp. 445–448, September–October, 1993.     

Features of a theoretical description of ionization potentials of the LiF molecule and electron affinity of the F atom

We have performed calculations of the ionization potentials of the LiF molecule and the electron affinity of the F atom (as the ionization potential of F^–) by the Green's function method in the approximation adapted for calculation of the ionization potentials for ionization from upper MO's and the ADC(3) approximation. We have shown that quantitative agreement with experimental values can be obtained only as a result of infinite partial summation of diagrams in the ADC(3) scheme.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 723–726, November–December, 1990.     

Enhancement of phenols on ion-pair extraction of chromium(VI) with tetraphenylarsonium

The effect of phenols on the ion-pair extraction of chromium(VI) as chromate anion (HCrO ₄ ^– ) with tetraphenylarsonium cation (TPA⁺) has been investigated. By using TPACl, chromate is extracted as an ion-pair, TPA⁺·HCrO ₄ ^– , into organic solvents, but its extractability into nonpolar solvents such as carbon tetrachloride is very low. The addition of several phenols greatly enhances the extractability, e.g., the distribution ratio of chromium(VI) between carbon tetrachloride and water rises 5500-fold in the presence of 0.020M 3,5-dichlorophenol in the organic phase. The enhancement was larger when using more acidic phenols and less polar solvents. From the analysis of the extraction data for the 3,5-dichlorophenol-carbon tetrachloride system, it was shown that one molecule of chromate is extracted together with one TPA⁺ and 1–3 phenol molecules and the extraction constants were determined. The UV spectrum indicated the extracted species including chromate ester to the TPA⁺·ArOCrO ₃ ^– ·mArOH (m=1,2).     

Estimating the hessian for gradient-type geometry optimizations

Optimization methods that use gradients require initial estimates of the Hessian or second derivative matrix; the more accurate the estimate, the more rapid the convergence. For geometry optimization, an approximate Hessian or force constant matrix is constructed from a simple valence force field that takes into account the inherent connectivity and flexibility of the molecule. Empirical rules are used to estimate the diagonal force constants for a set of redundant internal coordinates consisting of all stretches, bends, torsions and out-of-plane deformations involving bonded atoms. The force constants are transformed from the redundant internal coordinates to Cartesian coordinates, and then from Cartesian coordinates to the non-redundant internal coordinates used in the specification of the geometry and optimization. This method is especially suitable for cyclic molecules. Problems associated with the choice of internal coordinates for geometry optimization are also discussed.Fellow of the Alfred P. Sloan Foundation, 1981–83